Men who have sex with men (MSM) account for nearly two-thirds of all new HIV infections in the United States (US) and young MSM (YMSM) are the only risk group experiencing an increase in HIV incidence.1,2 After diagnosis, many YMSM do not enter medical care, get prescribed antiretroviral therapy (ART), adhere to ART regimens or achieve viral suppression. Novel theory-based interventions that optimize engagement in care, ART uptake and ART adherence for HIV+ YMSM are urgently needed to achieve both individual and public health benefits. Our study will evaluate the efficacy Epic Allies, a theory-based mobile phone application (app) that utilizes game mechanics and social networking features to improve engagement in care, ART uptake, ART adherence and viral suppression rates among HIV+ YMSM. Social networking technologies enhance support and reduce social isolation,3-5 while game mechanics engage users to motivate and sustain behavior change. High mobile phone ownership among YMSM supports using intervention tools based in these familiar, available technologies. The app addresses the most common engagement and adherence barriers among youth is tailored for the target population and is customizable for individual users. Epic Allies targets HIV+ YMSM aged 16-24, who are new to care (naive) or non-adherent to ART. Funded by the National Institutes of Health, through a Phase I SBIR application we worked with programmers and designers at Caktus Consulting Group to develop and test the Epic Allies prototype and found it acceptable among a sample of HIV+ YMSM. Our current Phase II proposal has 3 aims: Aim 1: Refine Epic Allies for use in a clinic-based trial and expand the scope of the developed app to address engagement in care and ART uptake. Enhancements to the social networking features of the app will be made to ensure the communication and support needs of youth who are not currently on ART and those new to care are met. To inform these changes, we will conduct in-depth usability interviews with 8-10 YMSM not currently on ART and new to care. Aim 2: Test Epic Allies app among 300 HIV+ YMSM recruited from 14 Adolescent Trials Network (ATN) sites. We will conduct a 2-arm randomized controlled trial with measures at baseline 3, 6 and 12 months. Primary outcome measures will include engagement in care, ART uptake, medication adherence and viral load suppression. Aim 3: Conduct a process evaluation of Epic Allies including intervention acceptability, impact and long-term sustainability. Qualitative in-depth exit interviews (n=30) wil evaluate Epic Allies' acceptability with the target population and its potential to improve engagement in care, uptake of ART and adherence. This project has high public health impact as it will address the current gap in scientific knowledge regarding how to best assist YMSM who are newly diagnosed with HIV and those who have adherence difficulties in order to improve medical, psychological, and public health outcomes. Moreover, the creation of a novel technology based adherence tool could be easily adapted for other highly prevalent and costly chronic diseases.